1. Field of the Invention
The present invention relates to a fluid consumption amount-measuring method and an apparatus for the same, for measuring a consumption amount of a fluid such as compressed air in a fluid-operated apparatus.
2. Description of the Related Art
The fluid-operated apparatus is widely used, for example, in the production steps. Usually, the fluid-operated apparatus is constructed such that the pressure fluid is not consumed when the operation is stopped. However, in some cases, the pressure fluid leaks, for example, due to any damage of piping and packing.
A flow rate-measuring apparatus has been hitherto used in order to measure the consumption amount brought about by the leakage of the pressure fluid as described above. The flow rate-measuring apparatus includes, for example, differential pressure flow meters, ultrasonic flow meters, turbine flow meters, hot-wire flow meters, orifice flow meters, and float flow meters.
Explanation will now be made for a case in which the consumption amount of the pressure fluid is measured by using the differential pressure flow meter. As shown in FIG. 8, the flow rate-measuring apparatus 10 comprises a throttle 16 having a known cross-sectional area arranged between a pressure fluid supply source 12 for constructing a fluid pressure system 11 and a fluid-operated apparatus 14 as a measurement objective. Pressure gauges 18, 20 are connected on the upstream and downstream sides of the throttle 16 respectively. The amount of the pressure fluid passing through a throttle 22 arranged in the fluid-operated apparatus 14 corresponds to the consumption amount of the pressure fluid consumed by the fluid-operated apparatus 14.
When the consumption amount of the pressure fluid consumed by the fluid-operated apparatus 14 is measured, the pressure fluid supply source 12 is firstly operated to supply the pressure fluid via the throttle 16 to the fluid-operated apparatus 14. During this process, the pressure of the pressure fluid, which is measured by the downstream pressure gauge 20, is inversely proportional to the effective cross-sectional area of the throttle 22 of the fluid-operated apparatus 14. All of the pressure fluid, which flows through the fluid-operated apparatus 14, is supplied via the throttle 16. Therefore, the flow rate of the pressure fluid flowing through the throttle 16 is equal to the flow rate of the pressure fluid supplied to the fluid-operated apparatus 14.
Accordingly, the flow rate of the pressure fluid flowing through the throttle 16 is determined from the pressures of the pressure fluid measured by the pressure gauges 18, 20 respectively and the effective cross-sectional area of the throttle 16. The effective cross-sectional area of the throttle 22 is determined from the flow rate and the pressure of the pressure fluid measured by the downstream pressure gauge 20. Thus, it is possible to determine the flow rate, i.e., the consumption amount of the pressure fluid flowing through the throttle 22 of the fluid-operated apparatus 14, from the effective cross-sectional area of the throttle 22 and the pressure of the pressure fluid measured by the upstream pressure gauge 18.
However, it is considerably difficult to measure the consumption amount brought about by the leakage, by using the flow rate-measuring apparatus 10 as described above. That is, in order to measure the consumption amount of the fluid-operated apparatus 14 highly accurately, it is necessary to select the flow rate-measuring apparatus 10 which has a measuring range in conformity with the degree of the consumption amount. However, the degree of the consumption amount, which is brought about by the leakage of the fluid to be measured, is usually unclear.
Therefore, in order to select the flow rate-measuring apparatus 10 having an optimum measuring range, it is also considered that a trial and error process is performed to attach and detach one selected from a plurality of flow rate-measuring apparatuses 10 having different measuring ranges with respect to the fluid pressure system 11. However, the attachment and detachment operation is extremely complicated. Further, the flow rate-measuring apparatus 10 itself is considerably expensive. Therefore, such a process is not considered to be an appropriate practical method.
Further, as shown in FIG. 8, when the flow rate-measuring apparatus 10 is constructed and connected in series on the upstream stage of the fluid-operated apparatus 14 for constructing the fluid pressure system 11 to measure the consumption amount brought about by the fluid-operated apparatus 14, for example, it is necessary to set a small effective cross-sectional area of the throttle 16 of the flow rate-measuring apparatus 10 in order to measure a small consumption amount highly accurately. As a result, the flow resistance of the pressure fluid becomes large. Therefore, it is difficult to perform the driving operation by supplying a predetermined amount of the pressure fluid to the fluid-operated apparatus 14 while still installing such a flow rate-measuring apparatus 10 after the measurement of the consumption amount.
Another arrangement is known as shown in FIG. 9. That is, a stop valve 24 is provided between a pressure fluid supply source 12 and a fluid-operated apparatus 14. A bypass, which comprises a stop valve 26, a flow rate-measuring apparatus 10, and a stop valve 28, is provided between upstream and downstream portions with respect to the stop valve 24. In this arrangement, the stop valves 24, 26, 28 are switched so that the pressure fluid may be supplied to the fluid-operated apparatus 14 via the flow rate-measuring apparatus 10 when the consumption amount is measured, while a predetermined amount of the pressure fluid may be directly supplied to the fluid-operated apparatus 14 while still installing the flow rate-measuring apparatus 10 when the fluid-operated apparatus 14 is driven and operated.
However, even in the case of this arrangement, it is necessary to perform the operation for selecting the flow rate-measuring apparatus 10 having an optimum measuring range in order to measure the consumption amount highly accurately. Therefore, the problem described above cannot be solved.
The present invention has been made in order to solve the problems as described above, an object of which is to provide a fluid consumption amount-measuring method and an apparatus for the same in which the operation including, for example, attachment and detachment to a fluid pressure system is easy, and the consumption amount due to the leakage of a pressure fluid or the like can be easily measured, making it possible to perform highly accurate measurement irrelevant to the measuring range of the consumption amount.
According to the present invention, even when the measuring range of the consumption amount in the fluid-operated apparatus is unknown, the pressure values P1, P2, P3 on the downstream side of a stop valve are measured and calculated respectively. Thus, it is possible to conveniently measure the consumption amount of the pressure fluid flowing through the fluid-operated apparatus.
Any one of the pressure value P2 and the pressure value P3 may be determined earlier. When the pressure values P1, P2, P3 on the downstream side of the stop valve are measured respectively, then the pressure drop is increased, and the measurement time is shortened by previously releasing a part of the pressure fluid in a forcible manner by the aid of another valve having a known effective cross-sectional area.
According to another aspect of the present invention, it is unnecessary that the fluid consumption amount-measuring apparatus is provided at an intermediate portion of a piping tube extending from a pressure fluid supply source to the fluid-operated apparatus. Therefore, it is easy to attach and detach the fluid consumption amount-measuring apparatus.
According to still another aspect of the present invention, a plurality of sets of ON/OFF valves and nozzles are preferably provided in parallel. In this arrangement, the consumption amount of the pressure fluid is calculated by a calculating unit from a pressure value which is detected by a pressure-detecting member when all of the ON/OFF valves are turned OFF respectively, a total of effective cross-sectional areas of the nozzles connected to the ON/OFF valves which are turned ON when the plurality of ON/OFF valves are selectively turned ON, and a pressure value which is detected by the pressure-detecting member under this condition. By doing so, the effective cross-sectional area of the nozzle is switched to adjust the pressure to be detected by the pressure-detecting means, and thus it is possible to perform the measurement with an optimum pressure range, which is preferred.
Alternatively, it is also preferable that the measuring range is switched by connecting, to the ON/OFF valve, a nozzle having a variable effective cross-sectional area.
According to still another aspect of the present invention, a pressure fluid-discharging valve, to which another nozzle having a known effective cross-sectional area is connected, is preferably provided on the downstream side of the stop valve. In this arrangement, the consumption amount of the pressure fluid is calculated by the calculating unit on the basis of a difference in effective cross-sectional area between the nozzle connected to the ON/OFF valve and the another nozzle connected to the pressure fluid-discharging valve, and a pressure value obtained when the ON/OFF valve is turned OFF and a pressure value obtained when the ON/OFF valve is turned ON in a state in which a part of the pressure fluid of the another nozzle is released by fully opening the pressure fluid-discharging valve.